This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-287721, filed Sep. 21, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic disk drive having a single-pole perpendicular recording head and a perpendicular recording medium, and a position error signal generation method.
2. Description of the Related Art
In recent years, magnetic disk drives employing perpendicular magnetic recording that can increase the recording density as compared to longitudinal magnetic recording are becoming popular. An example of such a magnetic disk drive employing perpendicular magnetic recording performs perpendicular magnetic recording/reproduction by combining a composite head formed from a single-pole perpendicular recording head and magnetoresistance effect type reproduction head (GMR head or the like) and a two-layered perpendicular magnetic recording medium. FIG. 1 shows the head output terminal waveform of the servo section when data perpendicularly magnetically recorded on a recording medium by this scheme is read out.
AGC shown in FIG. 1 represents a portion for amplitude gain control. An SIM portion corresponds to a servo index mark that indicates the start of servo data. A CYL portion corresponds to servo cylinder information and servo sector number information. A PAD portion corresponds to data for timing adjustment. A to D portions correspond to A to D burst signals. Since the signals are read by a head for directly detecting the magnetic field of a GMR head or the like, a signal having a signal amplitude of xe2x88x921 is detected even at a portion without any magnetization reversal (CYL portion or D portion), as shown in FIG. 1 (for the descriptive convenience, the signal amplitude is normalized to xc2x11).
The A to D burst signals are recorded on a track as, e.g., a pattern shown in FIG. 2. In this example, the A and B burst signals are located with a xc2xd phase shift for the target track. The C burst signal is located on the target track without any shift. The D burst signal is located with a full phase shift from the target track. For this reason, in the head output terminal waveform shown in FIG. 1, the amplitudes of the A to D burst signals appear as xe2x88x921 to 0, xe2x88x921 to 0, xe2x88x921 to +1, and xe2x88x921, respectively.
FIGS. 3A and 3B are block diagrams showing circuits for generating a positioning signal by conventional schemes. FIG. 3A shows an analog differentiation scheme, and FIG. 3B shows a digital differentiation scheme.
Referring to FIG. 3A, a head 1 is a composite head. A single-pole perpendicular recording head is employed for recording, and a GMR head is employed for reproduction. A signal read from the head 1 has the waveform shown in FIG. 1. A head amplifier (IC) 2 amplifies the signal read from the head 1. Since the low-frequency cutoff frequency of the head amplifier 2 at this time is several hundred kHz to 1 MHZ, the head amplifier 2 passes no DC (Direct Current) component, and the baseline of the waveform varies.
A variable gain amplifier (VGA) 3 determines the gain for the output signal of the head amplifier 2 in accordance with the output signal from an amplitude gain controller (AGC) 4. The AGC circuit 4 controls the variable gain amplifier 3 such that the AGC portion shown in FIG. 1 has a predetermined amplitude. A low-pass filter (LPF) 5 reduces high-frequency noise in the output signal from the variable gain amplifier 3.
A differentiator 6 executes analog differential processing for the output signal from the low-pass filter 5 so as to eliminate the variation in baseline and equalize the output waveform from the head with a servo waveform for normal planar recording. The output waveform from the differentiator 6 is the same as the servo waveform for normal planar recording.
An analog/digital converter (ADC) 7 samples the output signal from the differentiator 6. The sampling frequency is about 10 times the burst signal frequency. A finite impulse response circuit (FIR) 8 generates a reproduced signal on the basis of the output signal from the analog/digital converter 7.
A servo demodulation circuit 9 obtains the absolute value of the signal sampled by the analog/digital converter 7 and adds the signals in each burst section, thereby demodulating the burst amplitude. The signals are added in order to improve the S/N ratio of a position signal by the integration effect. From the thus obtained burst signal, a position signal is calculated by (A burst signal amplitude xe2x88x92B burst signal amplitude)/(A burst signal amplitude +B burst signal amplitude).
In the digital differential scheme shown in FIG. 3B, a 1-D arithmetic device 10 as a digital differentiator is arranged in place of the analog differentiator 6 shown in FIG. 3A. In this case, the 1-D arithmetic device 10 is placed on the output side of the analog/digital converter 7 to execute 1-D arithmetic operation for the output signal from the variable gain amplifier 3, thereby executing digital differential processing.
As described above, to eliminate the variation in baseline and equalize the output waveform from the head with the servo waveform for normal planar recording, in the prior arts, the output from the head amplifier is differentiated. A position error signal is generated on the basis of the differentiated signal.
However, the differential processing increases noise in the high-frequency region of the signal, degrades the S/N ratio, and increase variance of the position error signal.
Accordingly, it is an object of the present invention to provide a magnetic disk drive and position error signal generation method which restores a head output terminal signal without a distortion without executing differential processing and thus generating a position error signal with less variance.
According to one aspect of the present invention, there is provided a magnetic disk drive comprising: a composite head formed from a single-pole perpendicular recording head which writes a signal on a perpendicular recording medium and a magnetoresistance effect type reproduction head; an amplifier which amplifies an output signal from the head; an analog/digital converter which samples the signal amplified by the amplifier; a DC component restoring circuit which restores a DC component removed by the amplifier using the signal output from the converter; a signal restoring circuit which restores the output signal from the head on the basis of the DC component restored by the DC component restoring circuit and the signal output from the converter; and a demodulation circuit which generates a position error signal on the basis of the output signal restored by the signal restoring circuit.
According to another aspect of the present invention, there is provided a position error signal generation method applied to a magnetic disk drive having a composite head formed from a single-pole perpendicular recording head which writes a signal on a perpendicular recording medium and a magnetoresistance effect type reproduction head, an amplifier which amplifies an output signal from the head, and an analog/digital converter which samples the signal amplified by the amplifier, the method comprising: restoring a DC component removed by the amplifier using the signal output from the converter; restoring the output signal from the head on the basis of the restored DC component and the signal output from the converter; and generating a position error signal on the basis of the restored output signal.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.